Armor

ABSTRACT

1. A lightweight armor plate comprising a mass of sintered hard substantially spherical ceramic balls disposed in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls, and means for rigidly supporting said balls in said pyramidal relationship.

United States Patent McDougal et a]. 1 Dec, 12, 1972 [54] ARMOR1,463,498 7/1923 Burgess ..89/36 Z [72] Inventors: John A. McDougal,Madison 2,738,297 3/1956 Pfistershammer ..89/36 A Heights; KarlSehwartzwalder, FOREIGN PATENTS 0R APPLICATIONS Holly, both of Mich.

17,224 1908 Great Britain ..144/12 Assignee= General Motors Corporation,227,168 8/1943 Switzerland ..109/84 Detroit, Mich. 365,140 12/1922Germany 144/12 F filed: Apnl 1963 Primary Examiner-Stephen C. Bentley[21] Appl. No.: 275,402 Attorney-A. F. Baillio, G. N. Shampo and PeterP.

. Kozak [52] US. Cl ..109/84, 89/36 A, 161/404 EXEMPLARY CLAIM [51] Int.Cl ..F41h 5/04 [58] Field of Search ..89/36; 114/12, 13; 161/207; Allghtwelght armor Plate comrgnsmg a mas s of 109/78, 80 82 85 tered hardsubstantially spherical ceramic balls disposed in contacting pyramidalrelationship whereby each ball is in contact substantially with at leastthree [56] References cued other balls, and means for rigidly supportingsaid balls UNYTED STATES PATENTS in said pyramidal relationship. 7

952,877 3/ 1910 Cowper-Coles ..89/36 A 8 Claims, 4 Drawing Figures I wlfl am v Fr i PI j ARMOR This invention relates to armor plate and moreparticularly to lightweight armor plate for use in armored vehicles orthe like. The armor plate of this invention has particular applicabilityin armored military and domestic vehicle construction where it is theconventional practice to use hardened steel armor plate. While theconventional steel armor plate has been quite satisfactory from thestandpoint of protection against typical projectiles such as .30 and .50caliber shells, the weight of the steel plate adds greatly to the weightof the vehicle to thereby reduce markedly its mobility and usefulness.

It is the basic object of this invention to provide an improvedlightweight armor plate which will effectively protect the vehicleagainst penetration by .30 caliber and similar projectiles which greatlyreduces the weight of the vehicle and improves its mobility. It is amore specific object of this invention to provide an improvedlightweight armor plate consisting essentially of a laminated or unitarystructure which includes a mass of closely packed hard ceramic spheresarranged and suitably supported in abutting pyramid relationship whichis backed up by a lightweight, energy absorbing, ductile layer. Anotherobject of the invention is to provide a laminated lightweight armorplate consisting of a hard ceramic layer backed up by a relatively soft,yielding, lightweight, energy absorbing, ductile layer. Other objectsand advantages will be apparent from the following detailed descriptionof the invention and the various embodiments thereof, reference beinghad to the accompanying drawings, in which:

FIG. 1 is an armor construction comprising a layer of hard alumina ballsencased in a metal mesh screen having an aluminum mass cast thereaboutincluding a relatively thick aluminum backing layer;

FIG. 2 is another embodiment of the invention in which the alumina ballsare arranged in pyramidal abutting relation backed up and bonded to abacking plate of aluminum;

FIG. 3 is a laminated armor plate consisting of a hard alumina platesandwiched between and bonded to plates of aluminum; and

FIG. 4 is a group of ceramic spheres arranged in pyramidal close packedrelation.

Referring to FIG. 1 of the drawings, the basic concept of constructioninvolved in the applicants inven tion is embodied in a plate consistingof the close packed layers of ceramic spheres l backed up by arelatively soft, ductile layer 12. As most clearly apparent from thesketch of FIG. 4, the ceramic spheres are arranged in a pyramidalfashion whereby a sphere 14 in an outer or upper plane is supported bythree spheres 16 in the next inner or lower plane. Each sphere 16 is inturn supported by three spheres 18 in the next lower plane.

I The ceramic spheres are especially strong in compression and arelocated on the projectile entry side of the plate. When struck by aprojectile, the closely packed structure causes a rapid distribution offorces in the lateral plane since each sphere in the outer plane issupported by three spheres in the next backing up plane. Calculationshows that for a force applied normal to the plate on a sphere in thefirst plane, each of the three spheres in the second plane will receivea normal force component which is approximately 30 percent of theoriginal whereas each of the seven spheres in the third plane receivesless than 9 percent of the original force. Thus, rapid and effectiveforce reduction is obtained. In addition a portion of the force isdissipated in the directions parallel to the plate.

The hard ceramic spheres in position on the entry side of the plate alsoserve to greatly reduce the effectiveness of the projectile by breakingit up or deforming it. In this way, its ballistic efficiency andpenetrating power are greatly reduced. For high energy missiles, theshattering of both the projectile and the uppermost ceramic layeraffords tremendous advantage of the absorption of energy.

The ceramic spheres are preferably formed of alumina in the form oftabular alumina or corundum. A superior ceramic is formed by mixing abatch consisting of 87 percent tabular alumina of which percent is minus325 mesh, 3 percent tricalcium phosphate as a flux and 10 percentKentucky ball clay No. 4. The mixed material is balled by means of arotating drum and fired at about 2,950 F.

In a first specific embodiment of the invention as shown in FIG. 1 afirst layer 14 of hard spherical tabular alumina balls having athickness of about one-half to five-eighths inch is arranged in :a planein pyramidal abutting relation over a second layer 16 of the ballsarranged in a second plane. These layers are encased in a stainlesssteel wire screen 19 of about 10 to 20 mesh. This assembly is cast in amass of aluminum consisting of 90 percent aluminum and 10 percentmagnesium to form a plate having a nominal thickness of about 1% inchesin which an aluminum alloy backing layer 12 is formed integrally withthe aluminum alloy matrix 22. The matrix 22 encases and supports theball layers 14 and 16 and the screen 19 in the plate. The area] densityis about 23.6 pounds per square foot.

In a second embodiment the plate is structurally the same as the firstembodiment except that the backup layer 12 and the matrix 22 are amagnesium alloy consisting of 96 percent magnesium, 3.5 percentzirconium and 0.5 percent minor impurities. The areal density is about20.6 pounds per square foot.

In a third embodiment as shown in FIG. 2 two layers 24 and 26respectively are arranged in pyramidal relationship as described inconnection with FIG. 1. Each alumina sphere is encased in a nickel shellexcept at the points at which the spheres abut one another. The nickelshell 28 is applied by arranging the spherical balls in the pyramidalarrangement and then subjecting the configuration to a nickel carbonylnickel coating process in which the structure is exposed to thermallydecompose nickel carbonyl under vacuum conditions as is well known inthe art. This process results in a 100 percent nickel shell of goodductility and toughness having extreme work hardening capabilities. Theresulting structure which may be described as a nickelalumina honeycombstructure is bonded to a onefourth inch $086 aluminum alloy plate 30 bymeans of a polysulfide plastic adhesive 32. The areal density is about22.3 pounds per square foot.

A fourth example which embodies the invention in its broad aspects isshown in FIG. 3 which consists of a one-eighth inch 5086-H34 aluminumalloy plate 34 bonded to a three-fourths inch hard alumina tile 36 bymeans of a polysulfide adhesive layer 38. This laminate is backed by aone-fourth inch thick 5086-Hl12 aluminum alloy plate 40 bonded theretoby the polysulfide adhesive layer 42. The areal density is about 17.4

. pounds per square foot.

The protection ballistics limit for each of the above embodiments wasdetermined with .30 caliber armor piercing M2 projectiles at zeroobliquity. As described below, these tests showed a marked improvementover presently used hardened steel armor plate. In general, these testsshowed a protection ballistics limit in the neighborhood of about 35percent greater than that of the conventionally used steel armor plateof the same weight which indicates that the areal density of armor plateto protect against the normal impact of this projectile at the muzzlevelocity of the service load may be reduced by approximately the samepercentage.

The term protection ballistics limit as used herein is defined as thecritical or limit velocity at which the specified projectile will beborderlined in penetrating the armor plate. A complete penetration ofthe projectile through the plate is considered to occur whenever afragment or fragments from either the impacting projectile or the armorare caused to be thrown back from the armor plate with sufficientremaining energy to pierce a sheet of 0.020 inch thick 2024-T3 aluminumalloy placed parallel to and six inches beyond the target. A flyingfragment with this amount of energy is normally expected to producelethal damage or its equivalent froma variety of mass-velocitycombinations. Any impact which rebounds from the armor plate, remainsembedded in the plate or passes through the plate, but with insufficientenergy to pierce the 0.020 inch thick aluminum alloy plate, is termed apartial penetration.

The procedure for testing the plates involved hand loading a pluralityof .30 caliber shells with varied amounts of powder and determiningtheir muzzle velocity in trial tests. These were then firedperpendicularly at the plates and their penetration was observed wherebytheir protection ballistics limit was determined.

A ballistics limit for the .30 caliber AP-MZ projectile at angle ofincidence was determined to be 3,288 feet per second. This compares witha ballistics limit of about 2,450 feet per second for typicalhomogeneous armor plate of equal weight. The mechanism of penetration ofthe projectiles in this plate was unusual. The hardened steel bulletcore was shattered into many irregular pieces of approximately the sizeof N0. 6 shot. This shattering of the core appeared to give radialvelocity to the jacket. The shattering of the core appeared to takeplace early .in the penetration as evidenced by fragments which came torest less than three-eights inch penetration from the original surface.Those fragments possessing sufficient energy after the break up of thecore proceeded to penetrate further, shattering and displacing theceramic rubble formed and deforming the backing aluminum plate. Thoseparticles having sufficient energy continued into the backing platewhere their energy was absorbed.

The mechanism of penetration of the second embodiment was similar tothat of the first except that a slightlymore extensive crushing of theceramic occurred. The ballistics limit of this plate was determined tobe 3092 feet per second.

The mechanism of penetration of the third embodiment was similar to thatof the first and second and the ballistics limit was found to be 3,200feet per second.

In the fourth embodiment a conical spalling of the alumina occurred withthe wide end of the cone being formed at the rear aluminum plateindicating that the impact of the projectile was spread over a largearea of the rear plate. The ballistics limit was determined to be inexcess of 2,750 feet per second which is markedly superior toconventional steel plate of equal weight. Although the test resultsgiven about are in relation to .30 caliber shells, similar improvementis obtained with regard to .50 and similar caliber projectiles over theconventional homogeneous steel plate.

Although in the embodiment set forth above two layers of the ceramicballs have been employed, armor plate including three or more layers ofthe ceramic balls may be employed for increased effectiveness inbreaking up the projectile. However, it may be observed that when theplate is struck by a projectile, it is in compression up to the neutralaxis of the plate and in tension beyond the neutral axis. Hence, theinclusion of the ceramic material is of little value beyond this pointand is preferably omitted for the sake of cost and weight economy. It isessential, however, that the material beyond the neutral axis have ahigh tensile strength to resist spalling. It is not particularlyimportant to the effectiveness of the plate whether or not the spacebetween the balls is filled with a matrix material. The primaryrequirement is that the balls be maintained in a pyramidal relationshipwithin the armor plate. It is to be noted that in the third embodimentthe ceramic spheres were held together by means of a nickel shell butthe voids in the close packed array were not filled. Since thisconfiguration has no detrimental effect on the ballistics properties ofthe plate, it may be concluded that the selection of the matrix for thatportion of the plate is of secondary importance and that preferablythese spaces be not filled for weight reduction purposes. In any eventthe matrix material should be highly resistant to spalling to avoid theformation of particles which may be thrown rearwardly. Other materialsincluding tough ductile synthetic resins, such as polyamide andpolyurethane'polymers, which have good energy absorbing characteristicsmay be used as the matrix material, and other strong and tough adhesiveresins such as epoxy adhesives may be employed to bond the backing plateto the alumina sphere structure. Although the preferred ceramic materialfor use as the projectile fragmentary layer is the alumina described iabove, other ceramic materials, such as silicon carbide,

2. A lightweight armor plate comprising a layer of sintered hardsubstantially spherical ceramic balls arranged in contacting pyramidalrelationship whereby each ball is in contact substantially with at leastthree other balls which is adapted to fragmentize a projectile on impacttherewith, said balls being rigidly supported in said pyramidalrelationship, said layer being attached to a tough ductile energyabsorbing backup layer adapted to prevent penetration by the projectilefragments.

3. An integral lightweight armor plate comprising a rigid layer ofsintered hard alumina adapted to fragmentize a projectile on impacttherewith interposed between and bonded to a pair of aluminum layers,one of said aluminum layers being adapted to backup said alumina layerand prevent penetration by the projectile fragments.

4. A lightweight armor plate comprising a mass of sintered hardsubstantially spherical alumina balls disposed in contacting pyramidalrelationship whereby each ball is in contact substantially with at leastthree other balls, said balls being cast in a matrix of aluminum andbacked up by a layer of aluminum of substantial thickness.

5. A lightweight armor plate comprising a mass of sintered hardsubstantially spherical alumina balls disposed in contacting pyramidalrelationship whereby each of said balls is in contact substantially withat least three other balls, means for rigidly supporting said balls insaid pyramidal relationship, and a backup layer of a ductile energyabsorbing material secured thereto, said alumina balls being operativeon impact with a projectile to fragmentize the projectile and saidbackup layer being effective to absorb the energy of the projectilefragments and prevent their penetration thereof.

6. A lightweight armor plate comprising a frontal projectilefragmentizing mass including at least two layers of sintered hardsubstantially spherical alumina balls disposed in contacting pyramidalrelationship whereby each ball is in contact substantially with at leastthree other balls, means enveloping said balls and rigidly supportingthem in said pyramidal relationship, and a projectile fragment retainingbackup layer of a ductile energy absorbing material secured thereto.

7. A lightweight armor plate comprising a frontal projectilefragmentizing mass including at least two layers of sintered hardsubstantially spherical alumina balls disposed in contacting pyramidalrelationship whereby each ball is in contact substantially with at leastthree other balls, a metal coating over said balls supporting them insaid pyramidal relationship, and a projectile retaining backup layer ofa ductile energy absorbing material adhesively secured to said metalcoated mass.

8. A lightweight armor plate comprising a frontal projectilefragmentizing mass including at least two layers of sintered hardsubstantially spherical alumina balls disposed in contacting pyramidalrelationship whereby each ball is in contact substantially with at leastthree other balls, a matrix of tough synthetic resin material supportingsaid balls in said pyramidal relationship, and a projectile retainingbackup layer of a ductile energy absorbing material secured thereto.

1. A lightweight armor plate comprising a mass of sintered hardsubstantially spherical ceramic balls disposed in contacting pyramidalrelationship whereby each ball is in contact substantially with at leastthree other balls, and means for rigidly supporting said balls in saidpyramidal relationship.
 2. A lightweight armor plate comprising a layerof sintered hard substantially spherical ceramic balls arranged incontacting pyramidal relationship whereby each ball is in contactsubstantially with at least three other balls which is adapted tofragmentize a projectile on impact therewith, said balls being rigidlysupported in said pyramidal relationship, said layer being attached to atough ductile energy absorbing backup layer adapted to preventpenetration by the projectile fragments.
 3. An integral lightweightarmor plate comprising a rigid layer of sintered hard alumina adapted tofragmentize a projectile on impact therewith interposed between andbonded to a pair of aluminum layers, one of said aluminum layers beingadapted to backup said alumina layer and prevent penetration by theprojectile fragments.
 4. A lightweight armor plate comprising a mass ofsintered hard substantially spherical alumina balls disposed incontacting pyramidal relationship whereby each ball is in contactsubstantially with at least three other balls, said balls being cast ina matrix of aluminum and backed up by a layer of aluminum of substantialthickness.
 5. A lightweight armor plate comprising a mass of sinteredhard substantially spherical alumina balls disposed in contactingpyramidal relationship whereby each of said balls is in contactsubstantially with at leasT three other balls, means for rigidlysupporting said balls in said pyramidal relationship, and a backup layerof a ductile energy absorbing material secured thereto, said aluminaballs being operative on impact with a projectile to fragmentize theprojectile and said backup layer being effective to absorb the energy ofthe projectile fragments and prevent their penetration thereof.
 6. Alightweight armor plate comprising a frontal projectile fragmentizingmass including at least two layers of sintered hard substantiallyspherical alumina balls disposed in contacting pyramidal relationshipwhereby each ball is in contact substantially with at least three otherballs, means enveloping said balls and rigidly supporting them in saidpyramidal relationship, and a projectile fragment retaining backup layerof a ductile energy absorbing material secured thereto.
 7. A lightweightarmor plate comprising a frontal projectile fragmentizing mass includingat least two layers of sintered hard substantially spherical aluminaballs disposed in contacting pyramidal relationship whereby each ball isin contact substantially with at least three other balls, a metalcoating over said balls supporting them in said pyramidal relationship,and a projectile retaining backup layer of a ductile energy absorbingmaterial adhesively secured to said metal coated mass.
 8. A lightweightarmor plate comprising a frontal projectile fragmentizing mass includingat least two layers of sintered hard substantially spherical aluminaballs disposed in contacting pyramidal relationship whereby each ball isin contact substantially with at least three other balls, a matrix oftough synthetic resin material supporting said balls in said pyramidalrelationship, and a projectile retaining backup layer of a ductileenergy absorbing material secured thereto.